The present invention relates to a light source position adjusting method capable of adjusting the position of a light source which is used in an image input apparatus for two-dimensionally reading an image born by a film original using an image sensor by subjecting the light source to shading correction using an output value obtained by reading the image projected from the light source irradiating the film original by the image sensor while putting on the light source so that the quantity of light irradiated onto the film original is uniformly balanced.
Images recorded on photographic film originals such as a negative film, a reversal film and the like are conventionally printed onto light-sensitive materials such as photographic papers and the like by so-called direct exposure. That is, a method in which an image born by an original film is projected onto the light-sensitive material for area exposure.
In contrast, recently under development are apparatuses making use of digital exposure, that is, digital photoprinters which photoelectrically read image information recorded on a film original, convert the thus read image into a digital signal and thereafter apply various steps of image processing to the digital signal to thereby provide recording image information. The image (latent image) is then recorded on a light-sensitive material by scan exposing it with recording light which is modulated in accordance with the image information, and a print is produced through development.
The digital photoprinter can freely perform editing and layout jobs for print images such as composition of a plurality of images to a composite image, division of a single image into segments, editing of characters and images and the like. Further, it can perform various types of image processing such as color/density adjustments, magnification adjustments, edge enhancement and the like and output prints which are freely subjected to editing and image processing in accordance with a specific use. Although conventional print systems employing the direct exposure cannot reproduce the entire image recorded on a film in such aspects as density resolution, color/density reproducibility and the like, the digital photoprinter can output a print in which the image recorded on the film is almost perfectly reproduced.
Further, since the digital photoprinter can record (store) the image information of the images recorded on respective films and image processing conditions to the image information to a memory device provided with the system and an external memory device such as a floppy disc and the like, there is an advantage that extra printing and other jobs can be accomplished without any films serving as originals. What is more, extra printing and other jobs can be performed in a rapid and efficient manner because processing conditions need not be set again.
Essentially, the digital photoprinter is composed of an image input apparatus for reading the image recorded on an original such as a film and the like, a set-up device for determining exposing conditions used when the read image is recorded by being subjected to image processing and an image recording device or scan exposing a light-sensitive material in accordance with the thus determined exposing conditions and subjecting it to development processing.
In the image input apparatus used in the digital photoprinter, reading light is irradiated to a film as an original so as to obtain projection light which bears the original image and the projection light is then projected onto an image sensor such as a CCD or the like to thereby read the original image photoelectrically. The thus read original image information (image data signal) is subjected to proper image processing and exposed and a light-sensitive material is subjected to exposure, printing, development and the like based on the original image information so that a hard copy on which the film original bearing image is reproduced can be obtained.
To obtain an output image (finished print) having good image quality, the image must be reproduced with properly balanced color and density. For this purpose, the image input apparatus must read the image in such a manner that the color and density thereof are kept in good balance. However, since the illuminance of the light emitted from the filament of a light source is generally varied, there is used diffused light which is diffused using a diffusing device such as a diffusion plate, a diffusion box or the like or an image data signal read from a film original by an image sensor or the like is subjected shading correction electrically or by software using the data signal of the image projected from a light source when no film original is loaded.
However, when it is desired to obtain an image of higher quality, there is a problem that even if the light obtained by diffusing light emitted from a light source by a diffusing device is used and an obtained image data signal is subjected to shading correction, the shading correction cannot be sufficiently performed. Although it is contemplated to perfectly diffuse the light emitted from the light source by the diffusing device, since the light must be caused to pass through many diffusion plates and irregularly reflected many times for the perfect diffusion, a problem arises in that an intensity of light necessary to read an image cannot be obtained because it is lowered in the above processes.
Further, there is a variation of the positions of the filaments of lamps with respect to the inserting pins of the lamps to the sockets of light sources, for example, the mounting legs of the lamps which are inserted into the sockets of the light sources and the variation is different among the individual lamps. As a result, the center of an optical axis set from the mounting port of a socket is dislocated from the center of the filament of a lamp, by which the quantity of light of the light source is shaded. Since the shading is different among respective light sources, when an image input apparatus to which very high image quality is required is used, the shading resulting from the variation of filament positions must be also corrected.
To deal with the above problems, when a lamp is mounted or replaced, it must be repeatedly performed such a procedure to a plurality of light source positions that the lamp is put on after it is mounted on a socket, a light source image is read by an image sensor through a lens unit and a best light source position is determined by comparing the thus obtained shading states of the light source images with each other. However, there is a problem that the repetition of the above job takes a long time when the cooling of the lamp and the like is taken into consideration and the job is very troublesome. In addition, since the light source used in the above image input apparatus requires a high intensity of light, a current of about 10 A flows to the filament, a large quantity of heat is generated and the temperature of the light source increases to about 100.degree. C.
Although the external cover of the image input apparatus is of course removed when the light source is mounted or replaced, there is a problem that it is dangerous to adjust the light source position by putting on the lamp for shading correction in the state that the exterior cover is removed, whereas it is troublesome to put off and cool the lamp and open and close the exterior cover each time the light source position is moved.
Although there is a regulation that the temperature of the exterior cover must be 60.degree. C. or less when it is composed of metal or 85.degree. C. or less when it is composed of resin to ensure that the user can safely perform a job in the vicinity of the external cover, since the temperature of the light source is increased to about 100.degree. C. when it is put on, a problem arises in that the regulation may not be satisfied when the exterior cover is located near to the light source.
Even if an optimum light source position where the output value from an image sensor is made uniform is determined by reading the shading state of a light source image by the image sensor by adjusting the light source position while repeatedly putting on and off the lamp of the light source as described above, if a variation is made to image sensors such as, for example, CCDs and the like when they are manufactured and the sensitivities of the CCDs themselves are varied (the variation of the sensitivities due to position), that is, the CCDs are shaded, there is a problem that the quantity of light irradiated onto the plane of a film original by the lamp of the light source is not made uniform and the shading of the light source itself is not accurately corrected.